Experimental study of quark gluon plasma with single photon measurement

2000年夏天，在RHIC上实现了Au核之间的碰撞，并开始了实验研究。本项目的目的是在RHIC的PHENIX实验中确认夸克胶子等离子体(QGP)的实现，并研究QGP的性质。主要设备是电磁量热计，以测量65个AGeV Au原子核之间碰撞发出的光子。通过光子测量，将确定中性介子的产额和光谱，最终目标是推导出单光子产额。建立了分析框架，该框架由通过高速网络连接的PC和RAID盘组成，高PT的中性介子主要是由部分粒子之间的散射产生的喷注的残余物产生的。在碰撞的初始阶段，当射流在高温下穿过物质时，由于强烈的相互作用，它会遭受巨大的能量损失。这一结果首次提供了喷流能量损失的证据。单光子是QGP的一个探测器，它直接从QGP中提供信息。该理论预测了巨大的光子产额，该理论假设由于胶子的贡献，热化速度很快。在这项研究中，没有观察到光子产额的大幅增加，这对模型构成了很大的限制。

In the summer of 2000, collisions between Au nuclei were realized at RHIC, and experimental studies have started. This project aims to confirm the realization of quark gluon plasma (QGP), and to study the properties of QGP, in the PHENIX experiment at RHIC. Primary device was a electro-magnetic calorimeter, in order to measure photons emitted from the collisions between 65 AGeV Au nuclei. With photon measurements, neutral pion yield and spectra would be determined and ultimate goal was to deduce single-photon yield. Analysis frame was constructed, which consists of PC's connected via high-speed network and RAID disks.Neutral pions with high pT are mainly produced as a residue of jets which are produced with the scattering between partons. Jet will suffer large energy loss due to strong interactions when it passes through the matter at high temperature in the initial stage of collisions. The result provided the first evidence of the jet energy-loss.Single photon is a probe of QGP, which directly provides information from the QGP. Large photon yield is predicted in the theory, which assumes fast thermalisation due to gluon contributions. Large enhancement in the photon yield was not observed in this study, which places strong restriction to the models.